1. Field of the Invention
This invention relates to warning or alarm systems and, more particularly, to an electrical device for use in signaling the presence of unwanted substances such as liquids near sensitive electrical equipment. This invention further relates to such systems that are capable of automatically shutting off electrical power to electrical equipment when liquid is sensed in the vicinity of the electrical equipment.
2. Background Art
U.S. Pat. No. 5,790,036 to Fisher et al disclosed an apparatus for detecting the presence of electrically conductive fluids, including urine and other body fluids such as exudate from wounds. The apparatus included a pair of spaced-apart electrodes covered by absorbent material, together with a housing containing a signaling device which produced a palpable vibration, a sound, a light, or a radio signal when fluid in the absorbent material provided a conductive path between the electrodes.
U.S. Pat. No. 2,874,695 to C. A. Vaniman disclosed an enuresis napkin assembly adapted to be worn upon the body of a sleeping child to wake the child in the event of any involuntary voiding of his bladder. The assembly comprised a self-contained power pack in electrical circuit with a vibrator and a napkin having a pair of juxtaposed electrodes spaced from each other by a moisture absorbent insulator. The electrodes and insulator were so arranged that the absorbent insulator were wetted by even a small discharge of urine.
U.S. Pat. No. 5,192,932 to Schwab disclosed a device for sensing the presence of liquids or other substances and warning of potential hazards. The device included a thin, flexible mat constructed of metalized sheets and included conductive and non-conductive portions and a sensitivity layer for adjusting the sensitivity of the mat. The device further included monitoring means for sensing changes in the electrical property of the mat and means to electrically connect the mat to the monitoring means. Upon sensing a change in the electrical properties of the mat, a warning device was activated by the monitoring means and the monitoring means deactivated the electrical equipment. The mat could be cut to change the size and shape.
U.S. Pat. No. 5,188,143 to Krebs disclosed a water leakage detector sensitive to the presence of moisture and adapted for installation around any cylindrical or other shaped water vessel. The detector had an elongated, flexible sensing strip comprising a pair of conductors separated by insulation. Each conductor included an electrode coupling with a wire lead extending via a cable to an electrical plug. A circuit housing was provided having an audible alarm operably connected to an electrical socket adapted to detachably connect with the plug.
U.S. Pat. No. 5,992,218 to Tryba et al. disclosed a water leakage protector apparatus for appliances subject to leakage. The apparatus included a first device for detecting water leakage from the water supply line coupled to the appliance and a second device for detecting water leakage from the appliance itself. A control apparatus was coupled to a valve, affixed to the water supply line, to control water flowing to the appliance, and the control apparatus was connected to a source of electrical power. The appliance was connected to the control apparatus to obtain electrical power for operation. The first and second sensing devices were coupled to the control apparatus so that when a water leak was detected by either the first or the second detecting device the control apparatus stopped the water from flowing in the water supply line and interrupted electrical power to the appliance.
U.S. Pat. No. 6,731,215 to Harms et al. disclosed a leakage response system for an appliance. A sensor was provided that included a mat that was constructed of top and bottom outer layers of electrically conductive fabric separated by a central nonconductive fabric layer, and a pair of fusing layers fusing the top and bottom layers to the central nonconducting layer. The sensor could also include a pair of conductive pins for installation into a surface for detecting moisture hidden within the surface. An alternate sensor mat included a pair of apertured foil conductive layers separated by a nonconductive layer, and a pair of fusing layers fusing the foil conductive layers to the top and bottom nonconductive absorbent layers.